It is desirable for a chassis for holding telecommunication circuit cards to support a high density of cards, yet the chassis must effectively dissipate heat developed during operation while containing the spread of flames should a fire be imposed within the chassis. The cards installed in the chassis perform electrical operations, such as signal transception and amplification that generate a significant amount of heat. Typically, a chassis is installed in a rack that contains several other chassis stacked above and below. The heat and flames that may develop within a chassis in the rack have the potential to harm circuit cards housed in the chassis above and below the chassis where the heat and/or flames emanate from, and the flames should be contained to avoid damaging cards in the other chassis.
The chassis must also provide external protection for the circuit cards it houses. Thus, the chassis cannot freely expose the circuit cards to areas outside the chassis when attempting to dissipate heat and flames. Additionally, the chassis must provide a structural interconnection that maintains electrical continuity between the circuit cards and external transmission mediums such as copper wires or fiber optic cables while facilitating insertion and removal of the cards. A sufficient structure must be used to facilitate this circuit card modularity, which further limits the chassis' ability to provide outlets for heat and flames.
Additionally, to reduce the chassis size for a given number of circuits, the circuit card density must be increased. Increasing circuit card density is difficult not only due to heat dissipation and potential flame spread, but also because of electromagnetic noise that must be contained. Generally, increasing circuit card density involves employing smaller cards, and smaller cards require higher component density within the cards. Achieving effective heat dissipation with adequate flame spread and electromagnetic noise containment may even be more difficult for smaller card designs with higher component densities.
Thus several factors must be accounted for in the chassis and card design. Chassis designs with large interior spaces for directing heat and flames away from circuit cards may be undesirable because the chassis may become too large when accommodating a high density of circuits. Chassis designs with open exteriors for directing heat and flames away from the circuit cards may be undesirable because the circuit cards may not be sufficiently protected from externalities such as falling objects or heat and flames spreading from a chassis positioned above or below in the rack. Card designs that are relatively large require a larger chassis to house the same quantity of cards.
Thus, there is a need for a chassis and card design whereby the chassis may contain a high density of readily removable circuit cards while providing effective heat dissipation and flame and electromagnetic noise containment.